Brachytherapy

What is brachytherapy?

Brachytherapy is a term derived from Greek meaning “therapy at a short distance.” It involves the medical use of radioactive isotopes internally within or near a tumour to provide a high dose of radiation to this area. The aim is usually to destroy the tumour completely and prevent it from coming back, or occasionally to shrink it. By applying the radiation directly into the area the oncologist wants to treat, it gives only a very low dose of radiation to the normal surrounding organs, and hence less side-effects. This is because the radiation does not need to travel through all the organs in order to eventually get to the tumour as it does with external beam therapy (which is delivered from a machine outside the patient). Unfortunately not all tumours are amenable to this type of treatment.

How does radiation destroy a tumour?

Brachytherapy is one type of radiation therapy. Radiation Therapy is a treatment modality, which uses ionising radiation (photons, electrons, protons, etc.) to treat malignant tumours. The way that this is achieved is by aiming the radiation at the tumour and the radiation causes DNA damage within the cancerous cells in order to take away the cell’s ability to divide and therefore the tumour dies.

The aim of radiation therapy is to treat the cancer by delivering a high dose of radiation to all the tumour cells effectively killing them. At the same time we endeavor to deliver as low a dose of radiation as possible to the surrounding healthy tissue to minimise morbidity from the treatment. In brachytherapy the radiation is delivered directly into the tumour, and it is thus able to deliver this high dose of radiation into the tumour and less dose to the surrounding tissues.

Types of Brachytherapy

Brachytherapy is used in the management of a number of malignancies, including cervical and endometrial cancer, prostate cancer, various head and neck cancers, sarcomas, breast cancer, oesophagus and rectal cancer.

There are two main types of brachytherapy, namely high dose rate and low dose rate. With high dose rate, tubes are placed in or around a tumour. These tube/s are then attached to an afterloader, which is a machine containing a radioactive isotope (see pic below). Due to the isotope emitting radiation fast, the treatment is referred to as high dose rate brachytherapy. Because the isotope emitting radiation fast, it does not need to stay in the tumour long in order to deliver the radiation. The oncologist works out how long the isotope needs to stay in various parts of the tumour to deliver enough radiation to kill off the tumour. Under computer guidance, the isotope is then moved within the tubes in the tumour according to the oncologist’s plan. This treatment is typically done daily for 2-5 times. The most common applications for it are in cancer of the cervix and endometrium.

The other common type of brachytherapy is low dose rate brachytherapy. Today, this is most commonly used in prostate brachytherapy. Here, radioactive seeds are inserted into the prostate in theatre under ultrasound guidance. The oncologist and physicist work out the optimal placement of these seeds in theatre, in order to provide a high dose of radiation to the prostate in order to cure the cancer. Because the seeds emit radiation slowly, the procedure is referred to as low dose rate brachytherapy. The seeds stay in the prostate permanently until they lose their radioactivity. However, high dose rate brachytherapy is more and more being used to treat prostate cancer.

Another type of low dose rate brachytherapy gaining popularity is therasphere treatment, where a catheter is inserted into a liver tumour in theatre, and microscopic radioactive seeds are injected into the tumour in order to clear the cancer.

Brachytherapy is a valuable tool in the oncologist’s armoury, but increasingly it is being replaced by more sophisticated external beam therapy, which, with the refined computer assisted radiation planning available today, can give high doses of radiation to the tumour, while keeping doses to the surrounding structures low, similar to brachytherapy.

Written by Dr Duvern Ramiah.

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